(a) Field of the Invention
The present invention relates to a field emission display (FED), and more particularly, to an FED that includes emitters made of a carbon-based material and a grid plate mounted between front and rear substrates.
(b) Description of the Related Art
A type of conventional FEDs employs a triode structure of cathode electrodes, an anode electrode, and gate electrodes. The cathode electrodes, an insulation layer, and the gate electrodes are formed in this order on a first substrate on which emitters are to be formed. Openings are then formed in the gate electrodes and the insulation layer to expose the cathode electrodes, after which emitters are formed on exposed surfaces of the cathode electrodes. Further, the anode electrode and phosphor layers are formed on a second substrate.
It is often difficult to manufacture such FEDs having the triode structure. For example, it is hard to avoid forming a short between the cathode electrodes and the gate electrodes while providing emitter material into the openings of the gate electrodes and the insulation layer. Further, when the electrons emitted from the emitters are formed into electron beams and travel toward the phosphor layers, a diverging force of the electron beams is increased by influence of a positive voltage applied to the gate electrodes such that the electron beams disperse.
In an effort to overcome the problem of electron beam dispersion, a mesh-type grid plate is mounted between the first substrate and the second substrate. The grid plate enables better focusing of the electron beams emitted from the emitters.
In addition to focusing the electron beams, the grid plate also prevents damage to the first substrate (including the emitters formed thereon) when arcing results from the high voltage applied to the anode electrode. However, in practice, many of the electron beams emitted from the emitters are unable to pass through the openings of the grid plate and also experience misdirection away from their intended paths. Picture quality is significantly reduced as a result.
This is of particular concern with the FED configuration shown in FIG. 13. In the FED of FIG. 13, gate electrodes 5 are first formed on a first substrate 3 on which emitters 1 are to be formed. An insulation layer 7 is formed on the gate electrodes 5, then cathode electrodes 9 are formed on the insulation layer 7. The emitters 1 are formed on the cathode electrodes 9.
With this FED structure, most electron beams are emitted from edges of the emitters 1 and at predetermined angles to the first substrate 3. The electron beams then either arc toward a second substrate 11 while passing through openings 13a of a grid plate 13 or fail to pass through the openings 13a and strike the grid plate 13.
Therefore, many of the electron beams strike the grid plate 13 and are prevented from further movement, strike the grid plate 13 and are deflected to travel along an altered path, or pass through one of the openings 13a of the grid plate 13 corresponding to a pixel adjacent to the intended pixel. If the emitter 1 from which the electron beam arrows are drawn in FIG. 13 is used as an example, the electron beams emitted from this emitter 1 land on a phosphor layer 15 of the intended phosphor to illuminate the same and also land on phosphor layers 15′ of pixels adjacent to the intended pixel to illuminate the same. Picture quality is reduced as the electron beams land on the phosphor layers 15′ of unintended pixels.
The conventional grid plate 13 has a minimal thickness of approximately a few tens to a few hundred micrometers, and includes a plurality of openings 13a, each of which corresponds to one of the pixel regions. Further, lower spacers 17 are mounted in non-pixel regions and between the first substrate 3 and the grid plate 13. The lower spacers 17 maintain a uniform gap between the first substrate 3 and the grid plate 13. The grid plate 13 vibrates in response to the successive collision of electrons thereon. The vibration of the grid plate 13 occurs because of the thinness thereof and because of the distance between the lower spacers 17.
FIG. 14 is a schematic view used to describe a vibration pattern of the grid plate 13. To describe the vibration of the grid plate 13, the vibration thereof between two fixed points 19 where a pair of the lower spacers 17 is positioned will be described. An amplitude of vibration p of the grid plate 13 increases as the distance between the lower spacers 17 is enlarged. In the case where the distance between the lower spacers 17 is a few tens of millimeters, the vibration frequency bandwidth of the grid plate 13 falls to the range of the audible frequency bandwidth such that noise is generated by the grid plate 13.
To solve the problem of vibration of the grid plate 13 and the resulting noise, it is necessary to increase the number of the lower spacers 17 to reduce the distance therebetween. However, a problem with this approach is that FED manufacturing is made difficult by the resulting complicated process of arranging the larger number of lower spacers 17.